AdwLeaflet: Add a signal to handle swiping on its own
In order to be able to "swipe back" in an AdwLeaflet, which does not use new page for every step, it would be good to allow the widget user to influence how the swiping is handled. It may help to fix gnome-software#1969 , where gnome-software has its own "Back" button and its own stack of places where to return.
I imagine this as a signal, which will be emitted before the actual swipe action, and when a signal handler returns TRUE
, with a meaning handled
, then the adwaita will not do the swipe, otherwise it can do whatever it wants to. That way it'll be possible to use the default implementation and overriding only the special states in the app.